Traditional manual, gauging devices and techniques for parts such as rounds of ammunition and cylindrical components of such rounds have been replaced to some extent by automatic inspection methods and systems as illustrated in U.S. Pat. Nos. 4,923,066; 6,959,108; 7,403,872; and 8,004,694. However, many manual gauging devices and techniques are still used despite having a number of shortcomings associated with them. U.S. Pat. Nos. 4,918,825; 5,301,436; 5,570,513; 6,397,720; 6,718,645; 7,403,872; and 7,716,845 discloses such devices and techniques.
A round of ammunition (often synonymously termed a “bullet” or a “cartridge”) normally includes a case which includes a primer, a quantity of powder contained within the case, and a projectile held in the open end of the case. Upon the striking of the primer by the firing pin of the weapon there is generated a flame which serves to ignite the powder within the case, generating gases which expand and propel the projectile from the muzzle of the weapon. Normally, the case is geometrically shaped and sized to be contained within the chamber of the weapon, and the projectile has dimensions which allows it to fit in the breech end of the barrel, and to eventually pass through the barrel upon firing of the round. For many rifles, for example, it is common to make the case of the round of ammunition of a size which will provide for the maximumization of the force with which the projectile is propelled from the weapon to the target. Thus, it is common, for a round for a given caliber weapon, to employ a case which will contain a maximum amount of powder, hence the case has a large diameter relative to the diameter of the projectile employed. This case then becomes the “standard” case for a particular caliber weapon and weapons of this caliber are chambered to accept this standard case. Standards for the shape and size of a cartridge for a given weapon, e.g. a rifle, of a given caliber are established and published by Sporting Arms and Ammunition Manufacturers Institute (SAAMI), as well as by NATO.
The overall length (i.e. OAL) of an ammunition cartridge is a measurement from the base of the shell casing to the tip of the bullet, seated into the casing.
Handloaded cartridges and commercially available cartridges for firearms are normally created with a maximum length standardized by SAAMI. A cartridge's overall length may be shorter than the maximum standard, equal to the standard, or sometimes even longer.
The maximum overall length is dictated by the need to fit into a box magazine of standard manufacture. For example, the 0.223 Remington cartridge, when loaded for use in the semi-automatic AR-15 rifle (or the military's M-16 rifle), has to fit into the removable box magazine for that rifle. This dictates that the cartridge's maximum overall length be no greater than 2.260″. However, for competition purposes during off-hand and slow fire prone match stages, the 0.223 Remington is loaded one cartridge at a time into the rifle's receiver. This allows for the cartridge to be longer than the standardized 2.260″ SAAMI maximum overall length. These cartridges can be safely loaded to a length that has the ogive portion of the bullet just touching the rifle's lands. Many competitive shooters will make these cartridges 0.005″ less than the truly maximum allowable overall length, for the sake of safety.
It is desirable for these single-loaded cartridges to have as little bullet jump as possible before the bullet's ogive begins to be engraved by the rifle's lands. This minimized bullet jump increases the accuracy of the rifle, all else being equal.
For some cartridges, headspace is measured from the face of the closed bolt of the firearm to a point where a circle of a certain size, called a datum circle, would intersect the cone of the shoulder on the chamber. FIG. 2 depicts a prior art headspace gauge, as shown in U.S. Pat. No. 7,716,845.
Variation of headspace of either sense can create significant problems. For example if the chamber headspace is not large enough the bolt will not then close completely on a rifle, automatic pistol, or shotgun cartridge.
The cartridge headspace may be found too great in some cases because the cartridge has been stretched (in the case of reloads) by firing it in a gun that had excess headspace. If the casing is then reloaded without full length re-sizing and an attempt is made to use it in a gun with tight headspace, it may be found impossible to close the bolt.
If there is excess headspace in a gun there may be ignition trouble (misfires or hang fires) because the firing pin may not be able to give the primer a proper blow. Also accuracy may be diminished with excess headspace.
Eccentricity of a projectile with respect to its case exceeding 0.025 mm may cause a deterioration of the firing precision that increases with the eccentricity. In this context, the eccentricity is defined as the angle between the longitudinal axis of the projectile and the case. Ideally, i.e. in the case of perfect concentricity, this angle is equal to zero.
As a practical matter, commercially available ammunition or ammunition components, like casings, bullets, primers, and propellant, are all made within certain tolerances set by their manufacturers. Therefore, while these components may be within the manufacturing tolerance, some of the components may be near the optimal specification while others may be very close to the outside tolerance.
For example, cartridge castings are optimally cylindrical in shape. Thus, if one imagines a longitudinal axis passing through the center of casing from the head of the casting extending out of the mouth of the casing, a cross-section of the casing taken anywhere along the axis, perpendicularly to the axis, would reveal that the axis is in the center of a circle, if the casing is optimally shaped. That is, the wall of the casing is “concentric.” However, perfect concentricity is rare; casings, bullets, and cartridges may exhibit one or more eccentricities. Thus, casings may be produced which have a “thin” side or a “thick” side, or bullets may be produced which deviate from a perfectly circular cross-section to produce a “high” area where two halves of a mold are joined. Such variations from the optimum are called “eccentricities.” One must consider the eccentricities if accuracy in shooting is to be attained.
“Runout” is a term which is soften used to describe eccentricities which affect the outer (external) surface of a cartridge casing, bullet, or other generally cylindrical object. Runout is a deviation from the midline axis (also known as the central longitudinal axis or the geometric axis) of the outside surface of a cylinder. For example, cartridge casing “runout” can involve a “banana shape” curve in which the casing is not a perfectly straight cylinder, but bends longitudinally. With this kind of runout, each cross-section may be perfectly circular, but eccentric or offset relative to the geometrical axis of the cartridge as a whole. “Banana shape” runout may be seen in fired cartridge casings (which are commonly cleaned, resized and reloaded), and typically becomes more pronounced with every firing.
“Egg-shape,” or out-of-round runout occurs when one transverse cross-section of a casing, bullet or cartridge is not circular. This eccentricity is typically local, and may occur at any one cross-section independently of its occurrence at any other cross-section. Having found egg shape at one point, one cannot predict what various degrees, shapes or orientation of deformity might be found elsewhere.
Head runout occurs when the head on a casing is not “square.” This condition occurs when the head of the casing (or more commonly, a portion of the head of the casing) is not perpendicular to the central longitudinal axis of the casing.
Yet another troublesome eccentricity occurs when the casing wall thickness is not uniform. When this occurs, a portion of the casing wall is thinner. Because the outer surface of the casing may be uniform, checking for runout will not reliably determine variations in casing wall thickness. If the casing is thinner in a certain area, that section of the wall may unevenly stretch upon firing in both width and length, and the whole casing may, after several uses, be distorted into a banana-like shape.
All of these eccentricities affect accuracy in shooting. With runout, the bullet can be misaligned off axis in the bore when the cartridge is chambered in the firearm. If the casing thickness varies, for example in the neck region where the bullet is lodged, the bullet can be laterally offset and again may be positioned in the bore off axis from the optimum position when chambered. As noted above, very small errors will spread the bullet trajectories. For accurate shooting, the casing, bullet and loaded cartridge should be true within 0.001 inch or less. FIG. 1 depicts a prior art cartridge runout fixture including a dial indicator gauge as shown in U.S. Pat. No. 5,301,436.
WO 2009/130062 discloses a method and a device for the optical viewing of objects and WO 2005/022076 discloses a part inspection apparatus using light line generators.
Other U.S. patent documents related to the invention include: U.S. Pat. Nos. 4,315,688; 4,598,998; 4,644,394; 4,831,251; 4,852,983; 4,906,098; 5,521,707; 5,608,530; 5,646,724; 5,291,272; 6,055,329; 6,708,071; 6,959,108; 4,983,043; 3,924,953; 5,164,995; 4,721,388; 4,969,746; 5,012,117; 7,684,054; 7,403,872; 7,633,635; 7,312,607; 7,565,216; 7,777,900; 7,633,046; 7,633,634; 7,738,121; 7,755,754; 7,738,088; 7,796,278; 7,684,054; and 7,812,970; and, U.S. published patent applications 2006/0248739 and 2010/0201806.